BARRIER FUNCTION AND HYDRATION 161 60 • 5O • 30 20 •P0.01 I ß Vehicle-Treated Y2-Treated Figure 1. Effect of a natural lipid mixture on barrier recovery in acetone-treated murine skin: 30 •1 of Y2 (1.6%) or vehicle was topically applied to acetone-treated mouse skin (2 x 3 cm2). The barrier function was determined by measuring transepidermal water loss immediately after acetone treatment and four hours after Y2 or vehicle application. Results are mean + SEM. human skin two and four hours after barrier disruption (Figure 2 four-hour data not shown). These results suggest, first, that an exogenous mixture of physiological lipids can influence barrier recovery in barrier-disrupted human skin, and second, that com- 4O 30 I'-I Vehicle-Treated(n=5) [] Y2-Treated(n=5) "-• 20 133-,: 10 0 ß Tape-Stripped Acetone-Treated Figure 2. Effect of a natural lipid mixture on barrier recovery in perturbed human skin: 40 Ixl of Y2 (1.6%) or vehicle was topically applied to acetone-treated or tape-stripped human skin (about 20 cm 2 area). Results are mean + SEM. Significant differences are for Y2- vs vehicle-treated site.

162 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS plex, naturally occurring lipids, with an optimized lipid ratio, can accelerate barrier recovery in human skin, as shown above for murine skin. EFFECT OF LIPIDS ON SKIN HYDRATION Studies in hairless mice. Prior studies have demonstrated both that ceramides influence the water-holding capacity of stratum corneum (15-18) and that glucosylceramides stim- ulate epidermal proliferation (19). There is little information about the effect of other physiological lipids, applied topically, on skin hydration. We next examined the effect of the major individual stratum corneum lipids, as well as Y2, on skin hydration in acetone-treated mouse skin. As shown in Figure 3, both fatty acid (palmirate) and ceramide increase skin capacitance two hours after application. Cholesterol worsens capacitance in comparison to the vehicle. A lipid mixture consisting of cholesterol, ceramide, and palmirate (molar ratio at 1:1:3) also increases skin capacitance. However, the most dramatic increase in skin capacitance occurs following topical application of Y2 (1.6%). These results suggest that certain stratum corneum lipids, i.e., fatty acids and ceramides, improve skin hydration, and that a topical lipid mixture (Y2), enriched in all three stratum corneum lipids, produces the greatest increase in skin hydration. ._ • • • - ._ • E • '- r- [3_ 0 • --- o ._1 -- Figure 3. Effect of physiological lipids and a natural lipid mixture on skin capacitance in acetone-treated mouse skin: 40 •tl of Y2 (1.6%), cholesterol (2%), galactocerebroside II (1%), palmirate (1%), or vehicle was topically applied to acetone-treated mouse skin (about 2 x 3 cm 2 area). The lipid mixture (1.1%) contains cholesterol, galactocerebroside II, and palmitate (1:1:3 molar ratio). Skin capacitance was mea- sured before and two hours after lipid or vehicle application. The data are expressed as percentage increase after lipid or vehicle application. Results are mean -+ SEM. Significant differences are in comparison with vehicle alone.